Process optimization and modeling of heavy metals extraction from a molybdenum rich spent catalyst by Aspergillus niger using response surface methodology

The present study examines the biorecovery of heavy metals from a spent refinery catalyst obtained from one of the oil refineries in Iran using Aspergillus niger. Bioleaching experiments were carried out in batch cultures using A. niger in the one-step process to mobilize Co, Mo and Ni from hazardous spent catalysts. Response surface methodology (RSM) was applied for the design and analysis of experiments with the optimization of pH, temperature, inoculum percentage, pulp density and rotation speed during the bioleaching of the metals. Experiments were designed as per the central composite design (CCD) technique. Three cubic mathematical models were derived for prediction of the responses. In process optimization, maximal values of Co, Mo and Ni recoveries were achieved as 71%, 69% and 46%, respectively, with a pH of 5.0, a temperature of 31 °C, a pulp density of 2 g/L, a rotation speed of 115 rpm, and using a 12% inoculum.